1. Field of the Invention
The present invention relates to an electrophotographic copying apparatus of the powder image transfer type having a rotary photoconductive drum and a slit exposure unit, and more particularly to a copying apparatus of this type in which a cleaning unit disposed within or close to the developing unit is adapted to clean the photoconductive drum during the second revolution thereof following the first revolution of the drum during which an image is formed.
2. Description of the Prior Art
Copying apparatuses of this type are disclosed, for example in Japanese Laid Open Patent Applications Nos. SH 52-117l36, and SHO 51-106440 and U.S. Pat. No. 4,074,934. Because the cleaning unit is positioned close to the developing unit or the magnetic brush of the developing drum used as a cleaning unit, such copying apparatuses have the advantages that the toner removed from the photoconductive surface can easily be reused and that the apparatus has an overall compact construction.
Such an apparatus nevertheless has drawbacks. When making one copy, it carries out the charging, exposing, developing and transferring steps during the first turn of the photoconductive drum and carried out a cleaning operation during the second turn of the drum, thus necessitating one more turn of the photoconductive drum for a copying cycle than in copying machines in which the developing unit and cleaning units are spaced relatively far from each other. Additionally, the copying operation, even when it is for making a copy of a small size original, requires two revolutions of the drum which has a circumference at least equal to the length of the largest copy size, with the result that the portion of the photoconductive member which is substantially unused for copying must be moved a great amount, which is inefficient.
Further, because the photoconductive drum is adapted to make two revolutions for each copying cycle, the front end of the image formed on the drum for each copy is always positioned on the same portion of the photosensitive surface. This leads to degradation of that portion, making the photoconductive member unserviceable after only a short period of time. Another serious objection is that when the drum is used for copying an original having an increased length after making a large number of copies having a short length, the deteroriation of the one portion of the drum will cause a difference in the quality between the front and rear portions of the reproduced image.